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Bottle Rocket
=Bottle Rocket= Materials Construction Fine tuning your rocket nozzle The nozzle throat size and mandrel greatly affect the performance of your rocket and in small rockets this can only be found by trial and error. The quality of your black powder also has an enormous impact on nozzle and mandrel design. Some powders have a very fast burn rate creating more pressure quicker requiring a larger nozzle opening and some powders have a slower burn rate requiring a smaller opening. A deeper mandrel will also generate more thrust as this creates a larger surface area for the burn resulting in more powder being burnt at ignition time. Too deep, and the rocket will explode on the launch pad, too shallow and take-off will be very slow which will not allow the rocket to reach a proper altitude (having burnt most of its propellant even before it gains sufficient thrust to take off). So as you can see there are many factors that will affect the performance of your rocket, just keep experimenting and eventually your rocket will fly fast and high. Rocket Stabilization Now that you have built your rocket, it needs to be stabilized during it's flight time (in other words it needs to fly vertically). This control of your rocket is essential, not only for the safety of you or your audience but for your satisfaction. Especially if you have a payload attached, this needs to explode high in the sky and not on or near ground level. At all times we want to avoid injury or possibly starting a fire. Stabilizing your rocket is relatively a simple process as long as you follow these rules. Your stick needs to be straight and it needs to be long and heavy enough to pass the balance test. This test is simple, attach a stick to the side of your finished rocket and try and balance your rocket on your finger. Do this by placing your finger just behind the exhaust nozzle. If the rocket topples forward, then your stick is not long or heavy enough and may cause it to fly in unpredictable directions. If it topples backwards then your stick is too long or heavy and will make your rocket sluggish and reduce it's apogee. If it's too long simply trim a small amount off and do the test again. If it's not long or heavy enough replace the stick with a larger one. Also, if you have for example 2 sticks, which both pass through the balance test, but one is longer and lighter and the other one is shorter and heavier, it's the best to pick the longer lighter stick, so that you rocket will fly better. Basically the end result you are after is a rocket and stick that balance nicely on your finger when it is placed behind the nozzle. It's a simple process that will ensure your rocket will fly straight into the night sky and join the stars. Adding A Payload To Your Rocket Drill a small hole--2mm works well--into the rocket's end plug and just barely into the propellant. As the rocket consumes the last of its fuel, the propellant will ignite the effect charge through this hole. The high pressure inside the casing will push hot gas and sparks through this hole and so its best made near the side of the casing. The hole should not be set in the center because the flame front propagating through the propellant grain will reach this point first. The fire transfer hole in the end plug is primed with a bit of loose black powder, and the shell is attached to the casing with tape or hot glue. The time fuse of the shell must be adjusted for this purpose. Normally, the fuse of shells is long enough to allow the shell to reach maximum altitude when shot from a mortar . When used as a heading for a rocket as shown here, we would like the shell to explode virtually immediately when ignited since the rocket itself already provides the delay. A small amount of visco can be used, with 5mm giving a delay of less than half a second